In order to provide a tool, which is useful for synthesizing hull forms leading to superior seakeeping performance in the early stages of high-speed craft design, the authors propose some regression equations to evaluate the seakeeping performance of high-speed crafts of a hard-chine type, by means of some simple hull form parameters. Several years ago, one of the authors and Prof. M. Fujino developed a practical method for calculating vertical motions and wave loads of a high-speed craft travelling in head sea, and verified its validity by comparing the computed results with those of model tests. In this paper, the above-stated method is applied to calculate the vertical motions of 20 hard-chine-type data base hulls in head sea, and the obtained motion responses are classified into several groups by using correlation analysis. Then following Bales' procedure, a number of seakeeping performance ranks connected with these groups of motion responses are found. Finally, the relations between these performance ranks and hull form parameters are established by using regression analysis. Through the present rank equations, the effect of hull form parameters are clarified and the guidelines for improvement of seakeeping performance are also presented. Furthermore, the influence of ship speeds are also discussed.